The present invention relates to directly imageable planodgraphic printing plate precursor, sometimes referred to as xe2x80x9craw platexe2x80x9d, which can be directly processed by laser light and, in particular, it relates to a directly imageable waterless planographic printing plate precursor which enables printing to be conducted without using dampening water.
The direct manufacture of an offset printing plate from an original image without using a plate making film, that is to say directly imageable plate making, is beginning to become popular not only in short run printing fields but also more generally in the offset printing and gravure printing fields on account of its special features such as its simplicity and lack of requirement for skill, its speediness in that the printing plate is obtained in a short time, and its rationality in making possible selection from diverse systems according to quality and cost.
In particular, very recently, as a result of rapid advances in output systems such as prepress systems, image setters and laser printers, etc, new types of various directly imageable planographic printing plates have been developed.
Classifying these planographic printing plates by the plate making method employed, such methods include the method of irradiating with laser light, the method of inscribing with a thermal head, the method of locally applying voltage with a pin electrode, and the method of forming an ink repellent layer or ink receptive layer with an ink jet. Of these, the method employing laser light is more outstanding than the other systems in terms of resolution and the plate making speed, and there are many varieties thereof.
The printing plates employing laser light may be further divided into two types, the photon mode type which depends on photo-reaction and the heat mode type in which light-to-heat conversion takes place and a thermal reaction brought about. In particular, with the heat mode type there is the advantage that handling is possible in a bright room and, furthermore, due to rapid advances in the semiconductor lasers which serve as the light source, recently a fresh look has been taken at the usefulness thereof.
For example, in U.S. Pat. No. 5,339,737, U.S. Pat. No. 5,353,705, U.S. Pat. No. 5,378,580, U.S. Pat. No. 5,487,338, U.S. Pat. No. 5,385,092, U.S. Pat. No. 5,649,486, U.S Pat. No. 5,704,291 and U.S. Pat. No. 5,570,636, there are described directly imageable waterless planographic printing plate precursors which use laser light as the light source, together with their plate making methods.
The heat sensitive layer in this kind of thermal-breakdown type printing plate precursor uses primarily carbon black as the laser light absorbing compound and nitrocellulose as the thermally-decomposing compound and has, applied to its surface, a silicone rubber layer. The carbon black absorbs the laser light, converting it into heat energy, and the heat sensitive layer is broken down by this heat. Moreover, finally, these regions are eliminated by developing, as a result of which the surface silicone rubber layer separates away at the same time and ink-receptive regions are formed.
However, with these printing plates, since the image is formed by breakdown of the heat sensitive layer, the image ditch cells are deepened, so that problems arise in that the ink receptiveness at the minute halftone dots is impaired and the ink mileage is poor. Furthermore, in order that the heat sensitive layer readily undergoes thermal breakdown, a crosslinked structure is formed and so there is also the problem that the durability of the printing plate is poor. If the heat sensitive layer is made more flexible, the sensitivity drops markedly and indeed making the heat sensitive layer flexible has been difficult. Moreover, with such a printing plate, the sensitivity being low, there is also the problem that a high laser intensity is needed to break down the heat sensitive layer.
In JP-A-09-146264, there is proposed a negative type laser-sensitive waterless planographic printing plate precursor which has, in the light-to-heat conversion layer, a compound which converts laser light to heat, a polymeric compound with film forming capability, a photopolymerization initiator and an ethylenically unsaturated compound which can be photopolymerized, and by carrying out exposure of the entire face by UV irradiation following the formation of the silicone rubber layer, reaction takes place between the light-to-heat conversion layer and the silicone rubber layer.
In this printing plate, by carrying out exposure of the entire face following the application of the silicone rubber layer, the adhesive strength between the silicone rubber layer and the light sensitive layer is increased, with the result that a printing plate of outstanding image reproducibility and scratch resistance is obtained. However, as stated above, there is a trade-off between the flexibility of the light sensitive layer and sensitivity, and this has presented the problem in particular of low sensitivity.
In JP-A-09-239942, a peeling development type printing plate is proposed which contains, in a laser-responsive layer, a material which generates acid and a polymeric compound which is decomposed by the action of the acid, but since two steps are required, namely a laser irradiation step and a heating step, the process becomes more complex and there is also the inherent problem of peeling development in that the reproducibility of minute half tone dots is poor.
In U.S. Pat. No. 5,379,698 there is described a directly imageable waterless planographic printing plate which employs a thin metal film as a heat sensitive layer. With this printing plate, the heat sensitive layer is rather thin, so a very sharp image is obtained and this is advantageous in terms of the degree of resolution of the printing plate. However, the adhesion between the base material and the heat sensitive layer is poor and the heat sensitive layer in non-image regions separates away during the printing and this has presented the problem that ink adheres thereto, producing faults on the printed material. Moreover, with this printing plate, the image is also formed by breakdown of the heat sensitive layer, and again this presents the problem that the image ditch cells are deepened and the ink acceptance and ink mileage are impaired.
As well as the aforesaid negative type planographic printing plates, in particular in relation to directly imageable waterless planographic printing plates, positive type directly imageable waterless planographic printing plates may also be considered.
With this type of printing plate, the silicone rubber layer in the laser irradiated regions is selectively retained, and serves to provide the non-image regions. The mechanism thereof comprises some form of enhancement in the adhesive strength between the silicone rubber layer and laser-responsive layer due to the laser irradiation, or an enhancement in the adhesive strength of the laser-responsive layer and the substrate below, with the result that the unirradiated silicone rubber layer, or silicone rubber layer and laser-responsive layer, is/are selectively removed by the subsequent treatment.
The printing plate proposed in JP-A-09-120157 is one where an acid generated by laser irradiation acts as a catalyst to promote the reaction of the light sensitive layer, so that image reproduction is realized. However, a separate heat treatment step is necessary to promote the reaction following the acid generation, so the process becomes more complex. Moreover, following the acid generation, the time which elapses up to the heat treatment exerts an influence on the image reproducibility and this presents the problem that this image reproducibility is unstable.
The present invention seeks to provide positive and negative type directly imageable printing plate precursors which overcome the aforesaid disadvantages, do not require a complex process following the laser irradiation, and provide printing plates having high sensitivity and high image reproducibility.
In order to solve the abovementioned problems, the present invention provides a directly imageable planographic printing plate precursor having at least a heat sensitive layer on a substrate, which heat sensitive layer contains a light-to-heat conversion material and at least one organic compound containing a metal.
References herein to xe2x80x9cdirectly imageablexe2x80x9d indicate that the image forming is carried out directly from the recording head onto the printing plate precursor without using a negative or positive film at the time of exposure.
The directly imageable planographic printing plate precursors of the present invention are applicable to so-called waterless planographic printing plates which do not require dampening water or to so-called conventional pre-sensitized planographic printing plates which employ dampening water, but they can be particularly favourably used for waterless planographic printing plates.
Examples of the construction of a waterless planographic printing plate are the construction having a heat sensitive layer on a substrate and having an ink repellent layer thereon, the construction having a heat insulating layer on a substrate, with a heat sensitive layer thereon and furthermore having an ink repellent layer on this, or the construction which also have a protective film on these. As the ink repellent layer referred to here, there is preferably employed a silicone rubber layer.
Examples of the construction of a conventional pre-sensitized planographic printing plate precursor are constructions having a heat sensitive layer on a substrate, and having a hydrophilic layer as an ink repellent layer thereon, the construction having a hydrophilic layer as an ink repellent layer on a substrate and having a heat sensitive layer thereon, or having a heat sensitive layer on a hydrophilic substrate. As examples of the hydrophilic layer which serves as the ink repellent layer referred to here, there are polyvinyl alcohol and hydrophilic swellable layers, but from the point of view of ink repellency a hydrophilic swellable layer is preferred. Again, as the hydrophilic substrate referred to here, there is preferably used an aluminium substrate which has been subjected to a hydrophilicity-conferral treatment such as sand roughening or anodizing.
Next, explanation is given primarily of a directly imageable waterless planographic printing plate precursor but the present invention is not to be restricted thereto.
(a) Light to Heat Conversion Material
When utilising a printing plate precursor of the present invention, the image is formed by irradiating with laser light and so it is necessary to include a light-to-heat conversion material.
There are no particular restrictions on the light-to-heat conversion material provided that it absorbs laser light and, for example, it will be appropriate to use additives such as black pigments, e.g. carbon black, aniline black and cyanine black, green pigments of the phthalocyanine or naphthalocyanine type, carbon graphite, iron powder, diamine type metal complexes, dithiol type metal complexes, phenolthiol type metal complexes, mercaptophenol type metal complexes, inorganic compounds containing water of crystallization (such as copper sulphate), chromium sulphide, silicate compounds, metal oxides such as titanium oxide, vanadium oxide, manganese oxide, iron oxide, cobalt oxide and tungsten oxide, the hydroxides and sulphates of these metals, and metal powders of bismuth, iron, magnesium and aluminium.
Of these, carbon black is preferred from the point of view of its light-to-heat conversion factor, cost and ease of handling.
As well as the above materials, infrared- or near infrared-absorbing dyes can also be favourably used as the light-to-heat conversion material.
As these dyestuffs, there can be used all dyestuffs which has a maximum absorption wavelength in the range 400 nm to 1200 nm, but the preferred dyes are those used for electronics or recording, of the cyanine type, phthalo-cyanine type, phthalocyanine metal complex type, naphthalocyanine type, naphthalocyanine metal complex type, dithiol metal complex type (such as dithiol nickel complex type), naphthoquinone type, anthraquinone type, indophenol type, indoaniline type, indoaniline metal complex type, pyrylium type, thiopyrylium type, squarilium type, croconium type, azulenium type, diphenylmethane type, triphenylmethane type, triphenylmethane phthalide type, triallylmethane type, phenothiazine type, phenoxazine type, fluoran type, thiofluoran type, xanthene type, indolylphthalide type, azaphthalide type, chromenopyrazole type, leucoauramine type, rhodamine lactam type, quinazoline type, diazaxanthene type, bislactone type, fluorenone type, monoazo type, ketone imine type, disazo type, polymethine type, oxazine type, nigrosine type, bisazo type, bisazostilbene type, bisazooxadiazole type, bisazofluorenone type, bisazohydroxyperinone type, azochromium complex salt type, trisazotriphenylamine type, thioindigo type, perylene type, nitroso type, 1:2 metal complex salt type, intermolecular CT type, quinoline type, quinophthalone type and flugide type acid dyes, basic dyes, oil-soluble dyes, and triphenylmethane type leuco dyes, cationic dyes, azo type disperse dyes, benzothiopyran type spiropyran, 3,9-dibromoanthoanthrone, indanthrone, phenolphthalein, sulphophthalein, ethyl violet, methyl orange, fluorescein, methyl viologen, methylene blue and dimroth betaine.
Of these, cyanine dyes, azulenium dyes, squarilium dyes, croconium dyes, azo disperse dyes, bisazostilbene dyes, naphthoquinone dyes, anthraquinone dyes, perylene dyes, phthalocyanine dyes, naphthalocyanine metal complex dyes, polymethine type dyes, dithiolnickel complex dyes, indoaniline metal complex dyes, intermolecular CT dyes, benzothiopyran type spiropyran and nigrosine dyes, which are dyes employed for electronics or for recording, and have a maximum absorption wavelength in the range from 700 nm to 900 nm, are preferably used.
Furthermore, from amongst these dyes, those having a large molar absorptibility, formerly referred to as xe2x80x9cmolar extinction coefficientxe2x80x9d are preferably used. Specifically, xcex5 is preferably at least 1xc3x97104 and more preferably at least 1xc3x97105. This is because if xcex5 is smaller than 1xc3x97104, a sensitivity enhancement effect is difficult to realise.
Using such light-to-heat conversion materials on their own gives a sensitivity enhancement effect, but by jointly employing two or more types it is possible to further enhance the sensitivity.
Again, by jointly employing two or more light-to-heat conversion materials with different absorption wave-lengths, it is also possible to utilise with two or more types of laser with different emission wavelengths.
The light-to-heat conversion material content is preferably from 0.1 to 70 wt %, and more preferably from 0.5 to 40 wt %, in terms of the heat sensitive layer composition as a whole. If there is less than 0.1 wt %, no sensitivity enhancement effect in terms of laser light is to be seen, while with more than 40 wt % the durability of the printing plate tends to be lowered.
(b) Metal-Containing Organic Compound
The heat sensitive layer of a printing plate precursor of the present invention contains a metal-containing organic compound. The metal-containing organic compound may be a compound consisting of an organic portion and a central metal (i.e. disposed between respective organic groups or within an organic portion such as an organic ring) and may be a complex compounds in which there is co-ordinate bonding between the organic portion and the central metal or an organometallic compounds in which the central metal is covalently bonded to the organic portion. Inorganic compounds such as metal oxides do not fall within this category. These metal-containing organic compounds are characterized by the fact that they bring about a substitution reaction with compounds containing active hydrogen groups.
As examples of the central metal, there are the metals of Groups 2 to 6 of the Periodic Table. Of these, the metals of Periods 3 to 5 are preferred, with the Period 3 metal Al, the Period 4 metals Ti, Mn, Fe, Co, Ni, Cu, Zn and Ge, and the Period 5 metals In and Sn being particularly preferred.
Preferably, the metal-containing organic compound is a metal chelate compound.
Metal chelate compounds are formed between a chelate portion and an aforesaid metal at the centre (as explained above).
Specific examples of metal-containing organic compounds and types thereof which may be present in a heat-sensitive layer of a printing plate precursor embodying the invention are as follows.
(1) Metal Diketenates
These are metal chelate compounds in which the hydroxyl groups of the enol hydroxyl groups of diketones are substituted with a metal atom, and the central metal is bonded via oxygen atoms. Since there can also be co-ordination bonding of the diketone carbonyls to the metal, they are comparatively stable compounds.
Specific examples are metal pentanedionates (metal acetonates) in which the chelate portion is 2,4-pentadionate (acetylacetonate), fluoropentadionate, 2,2,6,6-tetramethyl-3,5-heptanedionate, benzoylacetonate, thenoyltrifluoroacetonate and 1,3-diphenyl-1,3-propane-dionate, metal acetoacetates in which the chelate portion is methylacetoacetate, ethylaceto-acetate, methacryloxyethylacetoacetate and acryloylacetoacetate, and salicylaldehyde complexes.
(2) Metal Alkoxides
These are compounds in which an alkyl group is bonded to a central metal via an oxygen atom. Examples are metal alkoxides in which the chelate portion is methoxide, ethoxide, propoxide, butoxide, phenoxide, allyloxide, methoxyethoxide or aminoethoxide.
(3) Alkyl Metals
These are compounds in which alkyl groups are directly bonded to the central metal and, in such circumstances, the metal is bonded to a carbon atom. Even where the organic portion compound is a diketone, if the metal is bonded at a carbon atom, then it is placed in this category. Amongst such compounds, acetylacetone metals are preferred.
(4) Metal Carboxylic Acid Salts
Examples include acetic acid metal salts, lactic acid metal salts, acrylic acid metal salts, methacrylic acid metal salts and stearic acid metal salts.
(5) Others
Examples of these include metal oxide chelate compounds such as titanium oxide acetonate, metal complexes such as titanocene phenoxide (diphenoxy, dicyclopentadienyl titanium) and heterometal chelate compounds with at least two types of metal atom in one molecule.
From amongst the above metal-containing organic compounds, the following can be given as specific examples of the metal-containing organic compounds which are preferably used.
As specific examples of organic compounds containing aluminum, there are aluminium isopropylate, mono sec-butoxyaluminium diisopropylate, aluminium sec-butylate, ethyl acetate aluminium diisopropylate, propyl acetate aluminium diisopropylate, butyl acetate aluminium diisopropylate, heptyl acetate aluminium diisopropylate, hexyl acetate aluminium diisopropylate, octyl acetate aluminium diisopropylate, nonyl acetate aluminium diisopropylate, ethyl acetate aluminium diethylate, ethyl acetate aluminium dibutylate, ethyl acetate aluminium diheptylate, ethyl acetate aluminium dinonylate, diethylacetate aluminium isopropylate, aluminium tris-(ethylacetoacetate), aluminium tris(propylacetoacetate), aluminium tris(butylacetoacetate), aluminium tris (hexyl-acetoacetate), aluminium tris(nonylacetoacetate), aluminium trisacetylacetonate, aluminium bisethylacetoacetate monoacetylacetonate, aluminium diacetylacetonate ethylacetoacetate, aluminium monoacetylacetonate bispropylacetoacetate, aluminium monoacetylacetonate bisbutylacetoacetate, aluminium monoacetylacetonate bishexylacetoacetate, aluminium monoethylacetoacetate bispropylacetoacetonate, aluminium monoethylacetoacetate bisbutylacetoacetonate, aluminium monoethylacetoacetate bishexylacetoacetonate, aluminium monoethylacetoacetate bisnonylacetoacetonate, aluminium dibutoxide monoacetoacetate, aluminium dipropoxide monoacetoacetate, aluminium dibutoxide monoethylacetoacetate, aluminium oxide acrylate, aluminium oxide octate, aluminium oxide stearate, trisalizarin aluminium, aluminium-s-butoxide bis(ethylacetoacetate), aluminium-s-butoxide ethylacetoacetate, aluminium-9-octadecenylacetoacetate diisopropoxide, aluminium phenoxide, aluminium acrylate and aluminium methacrylate.
As specific examples of organic compounds containing titanium, there are isopropyltriisostearoyl titanate, isopropyltri-n-stearoyl titanate, isopropyltrioctanoyl titanate, isopropyltridodecylbenzenesulphonyl titanate, isopropyl-tris(dioctyl pyrophosphite)titanate, tetraisopropylbis-(dioctyl phosphite)titanate, tetraoctylbis(ditridecyl-phosphite)titanate, tetra(2,2-diallyloxymethyl-1-butyl)-bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctylpyrophosphate)ethylenetitanate, tris(dioctylpyrophosphate)-ethylenetitanate, isopropyldimethacrylisostearoyltitanate, isopropylisostearoyldiacryltitanate, isopropyltri(dioctylphosphate)titanate, isopropyltricumylphenyltitanate, isopropyltri(n-aminoethylaminoethyl)titanate, dicumylphenyloxyacetate titanate, diisostearoylethylene titanate, isopropyldiisostearoylcumylphenyl titanate, isopropyldistearoylmethacryl titanate, isopropyldiisostearoylacryl titanate, isopropyl 4-aminobenzenesulphonyldi(dodecylbenzenesulphonyl)titanate, isopropyltrimethacryl titanate, isopropyldi(4-aminobenzoyl)isostearoyl titanate, isopropyltri(dioctylpyrophosphate)titanate, isopropyltriacryl titanate, isopropyltri(N,N-dimethylethylamino)titanate, isopropyltrianthranyl titanate, isopropyloctyl, butylpyrophosphate titanate, isopropyldi(butyl, methylpyrophosphate)-titanate, tetraisopropyldi(dilauroylphosphite)titanate, diisopropyloxyacetate titanate, isostearoylmethacryloxyacetate titanate, isostearoylacryloxyacetate titanate, di(dioctyl phosphate)oxyacetate titanate, 4-aminobenzenesulphonyldodecylbenzenesulphonyloxyacetate titanate, dimethacryloxyacetate titanate, dicumylphenolate-oxyacetate titanate, 4-aminobenzoylisostearoyloxyacetate titanate, diacryloxyacetate titanate, di(octyl, butylpyrophosphate)oxyacetate titanate, isostearoylmethacrylethylene titanate, di(dioctyl phosphate)ethylene titanate, 4-aminobenzenesulphonyldodecylbenzenesulphonylethylene titanate, dimethacrylethylene titanate, 4-aminobenzoylisostearoylethylene titanate, diacrylethylene titanate, dianthranylethylene titanate, di(butyl, methylpyrophosphate)ethylene titanate, titanium allylacetoacetate triisopropoxide, titanium bis(triethanolamine)diisopropoxide, titanium-n-butoxide(bis-2,4-pentanedionate), titaniumdiisopropoxidebis(tetramethylheptanedionate), titanium diisopropoxidebis(ethylacetoacetate), titanium methacryloxyethylacetoacetatetriisopropoxide, titanium methylphenoxide and titanium oxide-bis(pentanedionate).
Iron(III) acetylacetonate, dibenzoylmethane iron(II), tropolone iron, tristropolono-iron(III), hinokitiol iron, trishinokitiolo-iron(III), acetoacetic acid ester iron(III), iron(III) benzoylacetonate, iron(III) trifluoropentanedionate, salicylaldehydo-copper(II), copper(II) acetylacetonate, salicylaldehydoimine copper, copper kojate, biskojato-copper(II), tropolone copper, bistropolono-copper(II), bis(5-oxynaphthoquinone-1,4)copper, bis(1-oxyanthraquinone)nickel, acetoacetic acid ester copper, salicylamine copper, o-oxyazobenene copper, copper(II) benzoyl acetate, copper(II) ethylacetoacetate, copper(II) methacryloxyethyl acetoacetate, copper(II) methoxyethoxyethoxide, copper(II) 2,4-penanedionate, copper(II) 2,2,6,6-tetramethyl-3,5-heptanedionate, zinc N,N-dimethylaminoethoxide, zinc 2,4-pentanedionate and zinc 2,2,6,6-tetramethyl-3,5-heptanedionate are also favourably employed in the present invention.
Furthermore, salicylaldehydo-cobalt, o-oxyacetophenone nickel, bis(1-oxyxanthone)nickel, nickel pyromesaconate, salicylaldehydonickel, allyltriethyl germanium, allyltrimethyl germanium, ammonium tris(oxalate)germanate, bis[bis(trimethylsilyl)amino]germanium(II), carboxyethylgermanium sesquioxide, cyclopentadienyltrimethyl germanium, di-n-butyldiacetoxygermanium, di-n-butyldichlorogermanium, dimethylaminotrimethylgermanium, diphenylgermanium, hexaallyldigermoxane, hexaethyldigermoxane, hexamethyldigermanium, hydroxygermatrane monohydrate, methacryloxymethyltrimethylgermanium, methacryloxytriethylgermanium, tetraallylgermanium, tetra-n-butylgermanium, tetraisopropoxygermanium, tri-n-butylgermanium, trimethylchlorogermanium, triphenylgermanium, vinyltriethylgermanium, bis(2,4-pentanedionate)dichlorotin, di-n-butylbis(2,4-pentanedionate)-tin, calcium 2,4-pentanedionate, cerium(III) 2,4-pentanedionate, cobalt(II) 2,4-pentanedionate, cobalt(III) 2,4-pentanedionate, europium 2,4-pentanedionate, europium(III) thenoyltrifluoroacetonate, indium 2,4-pentanedionate, manganese(II) 2,4-pentanedionate, and manganese(III) 2,4-pentanedionate are also used in the present invention.
From amongst these metal-containing organic compounds,metal chelate compounds are preferably used and metal dikenates such as aluminium, iron(III) and titanium acetylacetonates (pentanedionates), ethylacetoacetonates (hexanedionates), propylacetoacetonates (heptanedionates), tetramethylheptanedionates and benzoylacetonates are particularly preferably used.
These metal-containing organic compounds can each be used on their own or they can be used in the form of mixtures of two or more types. The amount contained per 100 parts by weight of active hydrogen group-containing compound is preferably from 5 to 300 parts by weight, with from 10 to 150 parts by weight being further preferred. This is because if the amount is less than 5 parts by weight, then image formation becomes difficult, while with more than 300 parts by weight the properties of the heat sensitive layer tend to be lowered and problems tend to arise with the printing plate; such as for example problems in terms of printing durability.
When a printing plate precursor of the present invention is subjected to laser irradiation, heat is generated due to the action of the light-to-heat conversion material in the heat sensitive layer and, as a result of this heat, the metal-containing organic compound gives rise to reaction. In the case where the heat sensitive layer does not have a crosslinked structure, a positive type directly imageable waterless planographic printing plate is obtained. That is to say, the metal chelate compound in the regions which have undergone laser irradiation reacts and forms a crosslinked structure. As a result, in the laser irradiated regions, the adhesive strength between the silicone rubber layer and the heat sensitive layer is raised. On the other hand, in the un-irradiated regions, there is no such raising of the adhesive strength, so, by means of the subsequent developing treatment, there is elimination of the silicone rubber layer or of the silicone rubber layer and heat sensitive layer.
In the case where a crosslinked structure has already been formed in the heat sensitive layer, a negative type directly imageable waterless planographic printing plate is obtained. That is to say, the adhesive strength between the heat sensitive layer and the silicone rubber layer is lowered in the laser irradiated regions and, by means of the subsequent developing treatment, the silicone rubber layer is eliminated in those regions which have been subject to laser light irradiation. The detailed mechanism thereof is still unclear but it appears that, where a crosslinked structure has already been formed at the time of the plate processing, there is an elimination reaction due to the action of the heat produced by the laser irradiation. As a result, it is believed that the solvent resistance at the interface between the silicone rubber layer and the heat sensitive layer is altered and so there is specific elimination of the silicone rubber layer in the laser-irradiated regions during the developing treatment.
Just the silicone rubber layer or both the silicone rubber layer and the heat sensitive layer may be eliminated by the development, but it is preferred in terms of ink mileage that the heat sensitive layer remains.
(c) Active Hydrogen Group-containing Compound
In order to form a crosslinked structure with the metal chelate compound, it is preferred that the heat sensitive layer in the printing plate raw plate of the present invention also contains an active hydrogen group-containing compound. As examples of the active hydrogen group-containing compound there are compounds which contain a hydroxyl group, compounds which contain an amino group, compounds which contain a carboxyl group and compounds which contain a thiol group, but hydroxyl group-containing compounds are preferred.
Furthermore, the hydroxyl group-containing compounds may be either compounds which contain a phenolic hydroxyl group or compounds which contain an alcoholic hydroxyl group.
As examples of phenolic hydroxyl group-containing compounds there are the following compounds:
hydroquinone, catechol, guaiacol, cresol, xylenol, naphthol, dihydroxyanthraquinone, dihydroxybehzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, bisphenol A, bisphenol S, phenol formaldehyde novolak resins, resol resins, resorcinol benzaldehyde resins, pyrogallol acetone resins, hydroxystyrene polymers and copolymers, rosin-modified phenolic resins, epoxy-modified phenolic resins, lignin-modified phenolic resins, aniline-modified phenolic resins, melamine-modified phenolic resin and bisphenols.
Again, as examples of alcoholic hydroxyl group-containing compounds there are the following compounds:
ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 2-butene-1,4-diol, 5-hexene-1,2-diol, 7-octene-1,2-diol, 3-mercapto-1,2-propanediol, glycerol, diglycerol, trimethylolpropane, 1,2,4-butanetriol, pentaerythritol, dipentaerythritol, sorbitol, sorbitan, polyvinyl alcohol, cellulose and derivatives thereof, and hydroxyethyl (meth)acrylate polymers and copolymers.
Furthermore, it is also possible to use in the present invention epoxy acrylates, epoxy methacrylates, polyvinyl butyral resins and polymers into which hydroxyl groups have been incorporated by known methods.
From the point of view of their reactivity with the metal chelate compounds, compounds containing a phenolic hydroxyl group are particularly preferably used as the hydroxyl group-containing compound.
These active hydrogen group-containing compounds can each be used on their own or they can be used in the form of mixtures of two or more types. The amount incorporated is preferably from 5 to 80 wt % and more preferably from 20 to 60 wt % in terms of the heat sensitive layer composition as a whole. If the content is less than 5 wt % then the printing plate sensitivity is lowered while, conversely, if there is more than 80 wt % the solvent resistance of the printing plate tends to be reduced.
(d) Binder Polymer
From the point of view of the printing durability, the heat sensitive layer of the printing plate raw plate of the present invention preferably contains binder polymer. This binder polymer is not especially restricted provided that it is soluble in organic solvents and has a film-forming capability, but it is preferred that its glass transition temperature (Tg) be no more than 20xc2x0 C. and more preferably no more than 0xc2x0 C.
As specific examples of binder polymers which are soluble in organic solvents and have a film-forming capability and, furthermore, which also provide a shape-retaining function, there are vinyl polymers, unvulcanized rubber, polyoxides (polyethers), polyesters, polyurethanes and polyamides.
The binder polymer content is preferably from 5 to 70 wt % and more preferably from 10 to 50 wt % in terms of the heat sensitive layer composition as a whole. If less than 5% is incorporated, then the printing durability tends to be reduced whereas with more than 70 wt % the sensitivity tends to be lowered.
These binder polymers can be used singly or there can be used a mixture of several such polymers.
(e) Other Components
Additionally, where required, there may also be added levelling agents, surfactants, dispersing agents, plasticizers and other additives to the heat sensitive layer in the present invention.
The addition of coupling agents, such as silane coupling agents, can be carried out with considerable advantage to raise the adhesion properties in terms of the underlayer substrate or heat insulating layer.
Furthermore, in order to raise the adhesion properties in terms of the upper silicone rubber layer, there is also preferably added a silyl group-containing compound or an unsaturated group-containing compound. In particular, when the upper ink repellent layer is an addition type silicone rubber layer, there is preferably added a compound of the kind which contains both unsaturated and silyl groups. As specific examples of such compounds, it is possible to cite the compounds of the following structure. 
Here, R1, R2 and R3 are each a hydrogen atom, C1 to C20 substituted or unsubstituted alkyl group, substituted or unsubstituted phenyl group or substituted or unsubstituted aralkyl group, and they may be individually the same as or different from one another. L1 and L2 are each, independently of one another, a divalent linking group. Furthermore, n is 0, 1 or 2, and R4 is a C1 to C20 substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group or a vinyl group. X represents a hydrogen atom, halogen atom, xe2x80x94OCOR5 (acyloxy group) or xe2x80x94Oxe2x80x94Nxe2x95x90C(R6)(R7). Here, R5, R6 and R7 are C1 to C4 substituted or unsubstituted alkyl groups.
Preferably, the structure is such that at least one and more preferably at least two of R1, R2 and R3 are unsaturated groups.
With regard to the properties of the heat sensitive layer obtained in this way, from the point of view of the printing characteristics of the printing plate obtained it is preferred that the properties lie within a specified range. As examples thereof, there are the tensile properties, of which the initial elastic modulus in tension can be given as a typical example. Specifically, the initial elastic modulus of the heat sensitive layer in the printing plate, in tension, is preferably from 7 kgf/mm2 to 78 kgf/mm2 and more preferably from 10 kgf/mm2 to 65 kgf/mm2.
By setting the initial elastic modulus of the heat sensitive layer within the aforesaid range, it is possible to enhance the properties as a printing plate, in particular the printing durability. Conversely, if the initial elastic modulus is less than 7 kgf/mm2, the heat sensitive layer forming the image areas will tend to be sticky and pulling will tend to occur at the time of printing. Furthermore, in the case where the initial elastic modulus is more than 78 kgf/mm2, breakdown will tend to occur at the interface between the heat sensitive layer and the silicone rubber layer due to the repeated stress applied at the time of printing, and this lowers the printing durability.
With regard to the thickness of the heat sensitive layer, it is preferred that this be from 0.1 to 10 g/m2 as a covering layer from the point of view of the printing durability of the printing plate and also from the point of view of outstanding productivity in that the diluting solvent may be readily driven off. From 1 to 7 g/m2 is still further preferred.
For the silicone rubber layer employed in the printing plate precursor of the present invention, there can be used the silicone rubber layers utilized in conventional waterless planographic printing plates.
Such a silicone rubber layer may be obtained by lightly crosslinking a linear organopolysiloxane (preferably dimethylpolysiloxane), and a typical silicone rubber layer has repeating units of the kind represented by the following formula (I). 
Here n is an integer of 2 or more; and R is a C1-10 alkyl, aryl or cyano C1-10 group. It is preferred that no more than 40% of all the R groups be vinyl, phenyl, halo-vinyl or halo-phenyl, and that at least 60% of the R groups are methyl. Furthermore, there will be at least one hydroxyl group in the molecular chain, in the form of a chain terminal or pendant group.
As the silicone rubber in the present invention, it is possible to use a silicone rubber where condensation-type crosslinking of the following kind is carried out (RTV or LTV type silicone rubbers). That is to say, crosslinking is effected by condensation between the terminal groups represented by formula (II) and formula (III) or formula (IV). At this time there may also be present in the system excess crosslinking agent. 
were, R has the same meaning as R in formula I above; 
where, R has the same meaning as R in formula I above, and R1 and R2 are monovalent lower alkyl groups; 
where, R has the same meaning as R in formula I above and Ac is an acetyl group.
When carrying out such condensation type crosslinking, there may be added a catalyst such as a tin, zinc, lead, calcium, manganese or other such metal salt of a carboxylic acid, for example dibutyltin laurate, or tin(II) octoate or naphthenate, or alternatively chloroplatinic acid.
Besides this, adding a SiH group-containing polydimethylsiloxane or a silane (or siloxane) with a hydrolyseable functional group is also effective and, furthermore, with the objective of enhancing the rubber strength, there may be freely added known fillers such as silica.
Moreover, in the present invention, as an alternative, or in addition, to the aforesaid condensation type silicone rubber layer it is also possible to use an addition type silicone rubber layer. The use of an addition type silicone rubber layer is preferred from the point of view of the handling properties.
An addition type silicone rubber layer can be formed for example by applying, on the heat sensitive layer, a polyorganosiloxane with at least two vinyl groups in the molecule, a polyorganosiloxane with at least three SiH groups in the molecule and a platinum catalyst, diluted with a suitable solvent, and then heating and drying, and curing.
The organopolysiloxane with at least two vinyl groups in the molecule may have the vinyl groups either at the chain ends or along the chain and, as the organic groups other than alkenyl groups, substituted or unsubstituted alkyl groups or aryl groups are preferred. Furthermore, there may also be present a small amount of hydroxyl groups.
As specific examples of such polyorganosiloxanes with at least two vinyl groups in the molecule there are the following:
polydimethylsiloxanes with vinyl groups at both terminals, (methylvinylsiloxane)(dimethylsiloxane) copolymers with methyl groups at both terminals, (methylvinylsiloxane)(dimethylsiloxane) copolymers with vinyl groups at both terminals, compounds comprising two or more main chains of a polydimethylsiloxane with vinyl groups at both terminals and with dimethylene crosslinks between, (methyl 1-hexenesiloxane)(dimethylsiloxane) copolymers with methyl groups at both terminals and (methyl 1-hexenesiloxane)(dimethylsiloxane) copolymers with vinyl groups at both terminals.
From the point of view of the rubber properties after curing, these polyorganosiloxanes with at least two vinyl groups in the molecule preferably have a molecular weight of at least 5,000, and more preferably at least 10,000. Again, they can be used singly or a number can be mixed together in any proportions for use.
The polyorganosiloxane with at least three SiH groups in the molecule may have the SiH groups at chain terminals or along the chain and, as the organic groups other than SiH groups, substituted or unsubstituted alkyl groups or aryl groups are preferred.
As specific examples of such polyorganosiloxanes with at least three SiH groups in the molecule there are the following:
polydimethylsiloxanes with SiH groups at both terminals, polymethylhydrogensiloxanes with methyl groups at both terminals, (methylhydrogensiloxane)(dimethylsiloxane) copolymers with methyl groups at both terminals, (methylhydrogensiloxane)(dimethylsiloxane) copolymers with SiH groups at both terminals and cyclic polymethylhydrogensiloxane.
With regard to the proportions when using a mixture of the aforesaid vinyl group-containing polyorganosiloxane and SiH group-containing polyorganosiloxane, the preferred mixing proportions are such that, taking the number of vinyl groups in the silicone rubber composition as 1, the number of SiH groups is from 1.5 to 15 and more preferably from 1.5 to 12. If the proportion of SiH groups to vinyl groups is less than 1.5:1, then there is a tendency for the curing properties of the silicone rubber layer to be reduced, while if the proportion is greater than 15 then there is a tendency for the silicone rubber to become brittle and the wear resistance to be lowered, so this is undesirable.
As to the platinum compound which is preferably employed in the addition-type silicone rubber layer, examples include platinum per se, platinum chloride, chloroplatinic acid and olefin-coordinated platinum. Of these, olefin-coordinated platinum is preferred.
Again, with the objective of controlling the curing rate of the addition type silicone rubber layer, it is preferred that there be added a reaction inhibitor such as tetracyclo(methylvinyl)siloxane or other such vinyl group-containing organopolysiloxane, an alcohol with a carbon-carbon triple bond, acetone, methyl ethyl ketone, methanol, ethanol or propylene glycol monomethyl ether.
As well as these components, there may be added a hydroxyl group containing organopolysiloxane or hydrolyseable functional group containing silane (or siloxane) which are condensation type silicone rubber layer components, or for the purposes of raising the rubber strength there can be added a filler such as silica.
Moreover, in the present invention, as well as the above components, the silicone rubber layer preferably contains a silane coupling agent. Specific examples are acetoxysilanes, oximesilanes and alkoxysilanes, but an oximesilane with non-hydrolysing groups such as a vinyl group is particularly suitable. Preferably from 0.1 to 5 wt % and more preferably from 0.5 to 3 wt % of the silane coupling agent is used in terms of the solids component of the silicone rubber layer composition.
The film thickness of the silicone rubber layer is preferably from 0.5 to 20 g/m2 and more preferably from 0.5 to 5 g/m2. If the film thickness is less than 0.5 g/m2 the ink repellency of the printing plate tends to be reduced, while in the case of more than 20 g/m2, not only is this disadvantageous from an economic standpoint but also there is the problem that the ink mileage deteriorates.
Provided that it is a dimensionally stable sheet-like material, it is possible to use any metal or film as the substrate for the printing plate precursor of the present invention. As examples of such dimensionally stable sheet-like materials, there are those conventionally employed as printing plate substrates. These substrates include paper, plastic- (for example polyethylene, polypropylene or polystyrene) laminated paper, aluminium (including aluminium alloys), zinc, copper or other such metal sheet, films of plastics material, for example cellulose acetate, polyethylene terephthalate, polyethylene, polyester, polyamide, polyimide, polystyrene, polypropylene, polycarbonate or polyvinyl acetal, and also paper or plastics film laminated with, or with a vapour deposited coating of, an aforesaid metal.
Amongst these substrates, aluminium plates are especially preferred in that they have outstanding dimensional stability and, moreover, are comparatively cheap. Again, the polyethylene terephthalate films which are employed as substrates for short-run printing are also favourably used.
In order to prevent the heat due to the laser irradiation escaping into the substrate, it is effective to provide the printing plate precursor of the present invention with a heat insulating layer disposed between the substrate and heat sensitive layer.
There may also be used, typically, the primer layer hitherto employed for achieving firm adhesion between the substrate and heat sensitive layer.
The heat insulating layer used in the present invention needs to satisfy the following conditions. It will bond together well the substrate and the heat sensitive layer, and be stable with passage of time, and it will also be highly resistant to the developer and to the solvents used at the time of printing.
Examples of materials which satisfy such conditions include epoxy resins, polyurethane resins, phenolic resins, acrylic resins, alkyd resins, polyester resins, polyamide resins, urea resins, polyvinyl butyral resins, casein and gelatin. Of these, it is preferred that there be used polyurethane resins, polyester resins, acrylic resins, epoxy resins or urea resins, either singly or in the form of mixtures of two or more types.
Again, it is preferred that the image/non-image region contrast be enhanced by incorporating additives such as pigments or dyestuffs into this heat insulating layer.
The thickness of the heat insulating layer is preferably from 0.5 to 50 g/m2 and more preferably from 1 to 10 g/m2 as a coating layer. If the thickness is less than 0.5 g/m2, there is an inadequate shielding effect in terms of substrate surface shape defects and adverse chemical influences, while if the thickness is more than 50 g/m2 this is disadvantageous from economic considerations, and so the aforesaid range is preferred.
Explanation is now provided of the method of producing a directly imageable waterless planographic printing plate precursor of the present invention and the plate processing method.
On the substrate, using a normal coater such as a reverse roll coater, air knife coater, gravure coater, die coater or Meyer bar coater, or a rotary applicator such as a whirler, there is optionally applied a heat insulating layer composition and this is hardened by heating for a few minutes at 100 to 300xc2x0 C. or by actinic light irradiation, after which the heat sensitive layer composition is applied and dried by heating for from tens of seconds up to several minutes at 50 to 180xc2x0 C., and hardened where required.
Subsequently, the silicone rubber composition is applied and heat treatment carried out for a few minutes at 50 to 200xc2x0 C., to obtain a silicone rubber layer. Thereafter, where required, a protective film is laminated or a protective layer formed.
With the objective of protecting the silicone rubber layer on the directly imageable waterless planographic printing plate constructed as explained above, a plain or embossed protective film is laminated at the surface of the silicone rubber layer, or alternatively there may be formed as a protective film a polymer coating which dissolves in the developer solvent.
As examples of types of such protective film, there are polyester films, polypropylene films, polyvinyl alcohol films, saponified ethylene/vinyl acetate copolymer films, polyvinylidene chloride films and various types of metallized film.
The directly imageable waterless planographic printing plate precursor obtained in this way is subjected to image-wise exposure by means of laser light after separating off the protective film or from above the protective film.
As the laser light source employed in the plate processing light-exposure stage of the present invention, one with an oscillation wavelength region in the range 300 nm to 1500 nm is employed. Specifically, various lasers can be used such as an argon ion, krypton ion, helium-neon, helium-cadmium, ruby, glass, YAG, titanium sapphire, dye, nitrogen, metal vapour, excimer, free-electron or semiconductor laser.
Of these, for the purposes of processing the printing plate precursor of the present invention, a semiconductor laser of emission wavelength region in the vicinity of the near infrared region is preferred, with the use of a high output semiconductor laser being particularly preferred.
Following exposure, by employing a developing treatment, a printing plate on which an image pattern has been formed is produced by elimination of the unexposed regions in the case of a positive-type and by elimination of the exposed regions in a negative-type. Developing is carried out by a rubbing treatment in the presence or absence of water or organic solvent. Alternatively, developing is also possible by so-called peeling development where the pattern is formed on the printing plate by the peeling of the protective film.
As the developer used in the developing treatment for preparing a printing plate from a precursor embodying the invention, there can be employed, for example, water or water to which a surfactant is added, or such water to which an undermentioned polar solvent is also added, or at least one type of solvent such as an aliphatic hydrocarbon (e.g. hexane, heptane or isoparaffin type hydrocarbon), aromatic hydrocarbon (e.g. toluene or xylene) or halogenated hydrocarbon (e.g. Triclene), to which at least one undermentioned polar solvent is added.
As examples of the polar solvent, there are alcohols such as ethanol, propanol, isopropanol and ethylene glycol, ethers such as ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and tetrahydrofuran, ketones such as acetone, methyl ethyl ketone and diacetone alcohol, esters such as ethyl acetate, ethyl lactate and ethylene glycol monoethyl ether acetate, and carboxylic acids such as caproic acid, 2-ethylhexanoic acid and oleic acid.
Furthermore, there can be carried out the addition of surfactants to the aforesaid developer liquid composition. Moreover, there can also be added alkali agents such as sodium carbonate, monoethanolamine, diethanolamine, diglycolamine, monoglycolamine, triethanolamine, sodium silicate, potassium silicate, potassium hydroxide and sodium borate.
Of these, water or water to which surfactant has been added, and also water to which alkali has also be added, are preferably used.
Again, it is also possible to add to such developers known basic dyes, acid dyes or oil-soluble dyes such as Crystal Violet, Victoria Pure Blue or Astrazon Red, so as to carry out dyeing of the image region at the same time as the development or following development. By carrying out dyeing, discrimination between the regions eliminated by the development and the remaining regions is facilitated; i.e. the image/non-image region contrast is enhanced. The developing post-treatment liquids xe2x80x9cPA-1xe2x80x9d, xe2x80x9cPA-2xe2x80x9d, xe2x80x9cPA-Fxe2x80x9d, xe2x80x9cNA-1xe2x80x9d and xe2x80x9cWH-3xe2x80x9d, produced by Toray Industries Inc., can be given as preferred examples of the liquid employed in such dyeing.
At the time of the development, these developers can be used to impregnate a nonwoven material, degreased cotton, a cloth or sponge, and the developing carried out by wiping the plate surface.
Furthermore, the developing can also be satisfactorily carried out using a automatic developing machine as described in JP-A-63-163357 where, following pretreatment of the plate surface with an aforesaid developer, the plate surface is rubbed with a rotating brush while showering with, for example, tap water.
Instead of the aforesaid developer, development is also possible by spraying the plate surface with warm water or steam.